Adding metal treating agents to molten metal has undergone some degree of evolution within recent years to the point where such treating agents can be desirably added to the course of molten metal immediately before it reaches its casting cavity. Other stations for conventionally treating molten metal include in the furnace, in the ladle or holding unit, and in the stream as it is conveyed to a transfer ladle or dish. Treating agents can be used for a variety of purposes such as to alloy the base metal, inoculate or nodularize the base metal for purposes of producing a particular type of cast iron; a variety of other modes can create a change in chemistry of the base metal. One of the difficult aspects of adding such treating agents to molten metal, particularly in the furnace, is the inability to use a minimum amount that fully achieves solution; this is desirable because treating agents are typically highly expensive, they often go off into the slag, and may be lost by premature vaporization or oxidation. When the quanlity of base metal is large, the ability to homogenize or insure that all of the remote portions of the melt are affected by the treating agent is truly difficult.
Treating molten base metals in the ladle or in other holding units is somewhat better because the quantity of metal has been selectively reduced and because access is more convenient for purposes of stirring in the treating agent. If the treating agent is added to the mold, prior to pouring, the amount of treating agent will be more tailored to the specific quantity of metal cast and the furnace metal can be held in the untreated condition. Although the problems of volitization and pyrotechnics have been eliminated due to the closed condition of the mold which contains the treating agent, placed there in advance, several problems still remain. For example, the closed condition of the mold adds a degree of uncertainty as to reaction that is taking place out of sight of the operator. Each of the molds must be specially designed to receive the treating agent; any special modification of the mold line is economically unwelcome. Also, adding the agent to the mold prevents the mode from being adaptable to variations in base metal quality.
In some isolated instances, the industry has turned to steam treatment which involves injecting addition agents to a molten stream carried either in a closed trough or in an open spill way resulting from pouring a ladle. The stream is relatively low velocity since it is unnozzled and merely urged by gravity. In stream treatment, the art has employed rigid treating rods progressively inserted into the spill way stream or granular treating agents flowed into the stream.